This invention relates to a flywheel system for a rotary machine, such as an internal combustion engine.
Rotary shafts in a great number of machine aggregates exhibit rotational irregularities which may be caused by the system itself and/or by load conditions. Such rotational irregularities may be usually compensated for to a substantial extent by a flywheel which is the case, for example, in piston-type internal combustion engines. Thus, the periodic torque oscillations during a cycle of operation do not appreciably affect the machine assemblies connected with the rotary shaft.
Particularly in machine aggregates in which the rpm varies as a function of operational conditions, such as in internal combustion engines for vehicles, a relatively large flywheel mass is required for reducing rotational irregularities while the vehicle is stationary and thus the engine runs in a low rpm range, while, in contrast, at higher rpm's a lesser flywheel mass would be expedient. A large flywheel mass for the flywheel means, however, that during acceleration a correspondingly high energy input is required because apart from the required acceleration of the vehicle, the flywheel itself has to be accelerated as well.
To resolve the above-outlined problem, published European Application 0 612 915 suggests to associate a second flywheel with a first flywheel attached to the crankshaft of a vehicle engine. The second flywheel is mounted on the crankshaft for free rotation relative thereto and may be torque-transmittingly coupled by a frictional clutch to the first flywheel dependent upon operational conditions. Thus, by rendering effective the second flywheel, it is possible to provide a high flywheel mass in the low rpm range of engine run. Upon acceleration and in the high rpm range the second flywheel is uncoupled so that at lower rpm's the engine operates with acceptable irregularities, while engine acceleration occurs in a more vigorous manner. By connecting the second flywheel during braking, a better braking effect is achieved. A disadvantage of such an arrangement resides in the fact that by means of the frictional clutch which represents an additional component exposed to wear, the second flywheel may only be coupled to or uncoupled from the first flywheel so that additional shock phenomena appear.
For reducing the degree of rotational irregularities in an internal combustion engine, European Patent No. 0 338 485 discloses an electric motor/generator which is mechanically coupled with the engine, and by means of which, aided by appropriate circuit arrangements, a part of the engine torque may be absorbed or an additional torque may be applied to the engine as a function of the detected operational conditions. By an appropriate control of the motor/generator it is thus feasible to influence the degree of irregularity over the entire rpm range of the engine. It is a disadvantage of such an arrangement that additional forces have to be applied to the engine at the engine mounts, requiring additional structural measures.